Contact noise reduction



Dec, 19, 1961 J. BLOOMBERG 3,014,113

CONTACT NOISE REDUCTION Filed Feb. 6, 1961 O F WIRE B NKS O PILLAR OF COPOLYMER X VINYL CHLORIDE AND VINYLIDENE CHLORIDE F I j F I .2

IN V EN TOR. JEROME BLOOMBERG ATTORNEY United States Patent Ofiice ?atented Dec. 19, 1981 I 3,014,113 CONTACT NOIS REDUCTION Jerome Bloomherg, Rochester, N.Y., assignor to General Dynamics Corporation, Rochester, NFL, a corporation of Delaware Fiied Feb. 6, 1951, Ser. No. 87,349 3 Claims. (Cl. 200-466) The present invention relates to apparatus for maintaining contact noise in an electrical switching device at a minimum level.

In step by step telephone switching exchanges, contact noise is sometimes produced due to the presence of metallic oxides on the surfaces of the wires in the wire banks. It has also been observed that the presence of a high degree of moisture in the ambient atmosphere within these exchanges causes a considerable reduction of this contact noise. It is thought that this moisture increases the conductivity of the oxide film. One method of maintaining a high degree of humidity in the ambient atmosphere would utilize air conditioning apparatus which, of course, is relatively expensive. The present invention involves extremely inexpensive means for converting the aforementioned metallic oxides situated on the wire banks into hygroscopic metallic chlorides which absorb moisture from the ambient atmosphere. This conversion of the metallic oxide layer into a metallic chloride layer greatly reduces contact noise.

Accordingly, it is the object of the present invention to provide inexpensive and extremely effective apparatus for reducing contact noise in an electrical switching device.

Other objects, features and the attending advantages of the present invention will become apparent with reference to the following specification and drawings in which:

FIGS. 1 and 2 disclose a preferred embodiment of the present invention.

Referring now to FIG. 1 or" the drawing, an electrical switching device is disclosed in its home or at rest position. In this position, brush 1 is spring biased to contact pillar 2 which comprises a plastic of ccpolynier vinyl chloride and vinylidene chloride. When the switching device is operated, brush 1 leaves the home position as shown in FIG. 2 to sequentially contact contact members 3, which may be wires in the Wire banks of a telephone switching center. It has been found that during the molding of pillar 2 upon manufacturing, small quantities of hydrochloric acid are distributed within the pillar. When brush 1 leaves the home position, bits of minute particles are rubbed off pillar 2 thereby to deposit this plastic along with minute quantities of hydrochloric acid upon the tips of brush 1. Accordingly, extremely small amounts of hydrochloric acid are continuously deposited upon contact members 3 during the lifetime of the switch. The metallic oxides which are continuously formed on contact members 3 and which have a relatively high electrical resistance so as to produce contact noise are attacked by the acid and are converted into hygroscopic metallic chlorides. These salts absorb water from the air and are readily soluble in this water and the water produced by the aforementioned chemical reaction. Acoordingly, a new film is continuously produced having a greater ionization characteristic which results in increased electrical conductivity and greatly reduces contact noise.

Of course, the present invention is in no way restricted to step by step telephone switches but may be utilized in any electrical switch or distributor where contact noise 2 is to be maintained at a minimum level. The pillar of copolymer vinyl chloride and vinylidene chloride is readiiy moldable, is inexpensive and is commercially available. This material is marketed under the trademark Saran by Dow Chemical Company. It should be noted that the plastic material wears at a slow rate so that brush 1 may pass over the contact members hundreds of thousands of times without completely wearing away pillar 2. Minute particles of hydrochloric acid which. are distributed within pillar 2 are continuously deposited upon the contact members so that the metallic oxides which con tinuously form upon the contact members are converted into hygroscopic metallic salts to reducecontact noise over the entire lifetime of the switching device. I

Should pillar 2 wear down a new pillar may readily be substituted since the bottom portions of these pillars may be threaded.

While there has been disclosed What is at present considered to be the preferred embodiment of the invention, other modifications will readily occur to those skilled in the art. It is not therefore desired that the invention be limited to the specific arrangement shown and described and it is intended in the appended claims to cover all such modifications as fall Within the true spirit and scope of the invention.

What is claimed is:

1. An electrical switching device comprising, a first contact member, one or more second contact members, a part including copolyrner vinyl chloride and vinylidene chloride, means for causing said first contact member to contact said part during a first time interval and said second contact members during a second time interval to cause minute quantities of hydrochloric acid to be deposited on said second contact members to form hygroscopic metallic chlorides on said second contact members, thereby to reduce contact noise.

2. An electrical switching device comprising, a first contact member, one or more second contact embers, means for causing said first contact member to contact a part containing co-polymer vinyl chloride and vinylidene chloride while said first contact member is in its home position and for causing said first contact member to contact said second contact members at various times during the operation of said electrical switching device thereby to cause hygroscopic metallic chlorides to form on said second contact members to reduce contact noise over the lifetime of said electrical switching device.

3. An electrical switching device comprising, a first contact member, one or more second contact members, means for causing said first contact member to contact a stationary pillar containing copolymer vinyl chloride and vinylidene chloride while said first contact member is in its home position and for causing said first contact member to contact said second contact members at various times during the operation of said electrical switching device, thereby to cause hygroscopic metallic chlorides to form on said second contact members to reduce contact noise over the lifetime of said electrical switching device.

References Cited in the file of this patent UNITED STATES PATENTS 2,366,414 Lindh Ian. 2, 1945 2,964,436 Mikulis et a1 Dec. 13, 1960 FOREIGN PATENTS 684,473 Great Britain Dec. 17, 1952 

1. AN ELECTRICAL SWITCHING DEVICE COMPRISING, A FIRST CONTACT MEMBER, ONE OR MORE SECOND CONTACT MEMBERS, A PART INCLUDING COPOLYMER VINYL CHLORIDE AND VINYLIDENE CHLORIDE, MEANS FOR CAUSING SAID FIRST CONTACT MEMBER TO CONTACTA SAID PART DURING A FIRST TIME INTERVAL AND SAID SECOND CONTACT MEMBERS DURING A SECOND TIME INTERVAL TO CAUSE MINUTE QUANTITIES OF HYDROCHLORIC ACID TO BE DEPOSITED ON SAID SECOND CONTACT MEMBERS TO FORM HYGROSCOPIC METALLIC CHLORIDES ON SAID SECOND CONTACT MEMBERS, THEREBY TO REDUCE CONTACT NOISE. 